Researchers said that improving the accuracy of risk analysis using genetic screening could help breast cancer prevention and save lives.
Professor Douglas Easton, director of the Centre for Cancer Genetic Epidemiology at the University of Cambridge, one of the leaders of the study, said he hoped genetic risk prediction would become part of routine breast screening in future.
Currently only women with a family history of breast cancer are referred for genetic screening. Actress Angelina Jolie, whose mother died of ovarian cancer, has spoken of finding she carries a mutation in the BRCA1 gene, which significantly increases her chances of developing both breast and ovarian cancer. This led her to have a double mastectomy in 2013, and have her ovaries and fallopian tubes removed last month.
The study, published in the Journal of the National Cancer Institute, showed a test for differences in 77 separate letters of DNA code could indicate a woman’s risk of developing breast cancer, in women with or without a family history of the disease.
Researchers came up with a “polygenic risk score” for each woman based on their DNA code, and found those with a high score had a higher risk of breast cancer. A woman in the top 20 per cent for polygenic risk score was 1.8 times more likely to develop breast cancer than the average woman.
Meanwhile, a woman in the top 1 per cent for the polygenic risk score was three times more likely to develop breast cancer than average – corresponding to a risk for these women of around one in three.
The research, which looked at 65,000 European women, found that analysing this panel of 77 genetic markers was much more accurate in defining risk than previous tests that used fewer markers.
Lifetime risk of breast cancer for women with a history of it in close family was 24.4 per cent if they were in the highest-scoring fifth, against 8.6 per cent if they were in the lowest fifth. But for women without a history of breast cancer in their close family, the risks were 16.6 per cent and 5.2 per cent respectively.
Montserrat Garcia-Closas, professor of epidemiology at the Institute of Cancer Research, London, who also co-led the research, said: “Our study is the most definitive so far to show the clear benefits of using genetic testing for a large number of genetic risk factors in identifying women at elevated risk of developing breast cancer.
“This type of testing could fit alongside other standard risk measures, such as family history and body mass index, to improve our ability to target the best preventive treatments and advice to those women most likely to benefit from them.
“It’s now important to work out how this sort of test could be used widely in a healthcare, rather than in a research setting.”
Nell Barrie from Cancer Research UK said: “This study shows how the genetic map of breast cancer that scientists have been building up over the years might be used to identify women most at risk, so we can take steps to reduce their chances of developing the disease.”
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